194 DISTINCT SPECIES PRESENT [Chap. V. 



— that the great variability of secondary sexual charac- 

 ters, and their great difference in closely allied species; 

 — that secondary sexual and ordinary specific diilerences 

 are generally displayed in the same parts of the organisa- 

 tion, — are all principles closely connected together. 

 All being mainly due to the species of the same group 

 being the descendants of a common progenitor, from 

 whom they have inherited much in common, — to parts 

 which have recently and largely varied being more likely 

 still to go on varying than parts which have long been 

 inherited and have not varied — to natural selection hav- 

 ing more or less completely, according to the lapse of 

 time, overmastered the tendency to reversion and to 

 further variability, — ^to sexual selection being less rigid 

 than ordinary selection,— and to variations in the same 

 parts having been accumulated by natural and sexual 

 selection, and having been thus adapted for secondary 

 sexual, and for ordinary purposes. 



Distinct Species present analogous Variations, so that 

 a Variety of one Species often assumes a Character proper 

 to an allied Species, or reverts to some of the Characters 

 of an early Progenitor. — These propositions will be most 

 readily understood by looking to our domestic races/ 

 The most distinct breeds of the pigeon, in countries 

 widely apart, present sub-varieties with reversed 

 feathers on the head, and with feathers on the feet, — 

 characters not possessed by the aboriginal rock-pigeon; 

 these then are analogous variations in two or more 

 distinct races. The frequent presence of fourteen or 

 even sixteen tail-feathers in the pouter may be con- 

 sidered as a variation representing the normal structure 

 of another race, the fantail. I presume that no one will 

 doubt that all such analogous variations are due to the 



